What kind of diffuser are you using? Most put the diffuser on the side of the tank, for growth of plants probably hide the diffuser in time. Als it is best to have the diffuser as deep as possible, since the bubbles rise. Could you not put the spray bar on the bottom near the diffuser? It would help distribute the Co2.
Are you aware that UGF can get clogged up by plants. Thus it would better to make it a RUGF. You might be okay since the only root plants are the crypts.